Luting Cements Rola Shadid, BDS, MSc, Associate fellow AAID

Luting CementsLuting CementsLuting CementsLuting Cements

Rola Shadid, BDS, MSc, Associate Rola Shadid, BDS, MSc, Associate fellow AAIDfellow AAID

Key TermsKey Terms

Cement :Cement : Substance that hardens to act Substance that hardens to act as a base ,liner , filling material , or as a base ,liner , filling material , or adhesive to bind devices & prostheses adhesive to bind devices & prostheses to tooth structure or to each otherto tooth structure or to each other

Luting agent : Luting agent : A viscous material A viscous material placed between tooth structure & placed between tooth structure & prostheses that hardens through prostheses that hardens through chemical rxn to seal a space or to chemical rxn to seal a space or to cement two components together.cement two components together.

Key TermsKey Terms

Film thickness Film thickness : Height of space betw. two : Height of space betw. two surfaces that are separated by the cement surfaces that are separated by the cement layer. This dimension is measured after layer. This dimension is measured after pressure is applied betw. two flat surfaces that pressure is applied betw. two flat surfaces that are separated by a cement layer.are separated by a cement layer.

For temporary & final cementation, the For temporary & final cementation, the

maximum thickness is typicallymaximum thickness is typically about 40µmabout 40µm The size of particles & P/L ratio significantly The size of particles & P/L ratio significantly

affect FT.affect FT.

Continue/Continue/

A thinner film has fewer internal A thinner film has fewer internal flaws compared with a thicker one flaws compared with a thicker one ( increase retention)( increase retention)

Excess cement can be expressed Excess cement can be expressed more easily when thin film thickness more easily when thin film thickness is providedis provided

Key TermsKey Terms

Working timeWorking time: The time from the start of : The time from the start of mixing to the maximum time at which the mixing to the maximum time at which the viscosity of the mix is still low enough to viscosity of the mix is still low enough to flow readily under pressure to form a thin flow readily under pressure to form a thin filmfilm

Setting time Setting time :The elapsed time from the :The elapsed time from the start of mixing to a point at which an start of mixing to a point at which an external physical disturbance will not external physical disturbance will not cause permanent dimensional changecause permanent dimensional change

QuestionQuestion During the initial seating of During the initial seating of

three-unit bridge, if the three-unit bridge, if the prosthesis fits the prepared tooth prosthesis fits the prepared tooth perfectly that removal requires a perfectly that removal requires a

great deal of force .Why is a great deal of force .Why is a cement required for retention cement required for retention

under this condition ?under this condition ?

AnswerAnswer

When two flat surfaces are brought When two flat surfaces are brought into contact, a space exists betw. into contact, a space exists betw. them on a microscopic scale ; the them on a microscopic scale ; the surfaces exhibit peaks & valleys so surfaces exhibit peaks & valleys so there are only point contacts along there are only point contacts along the peaks. The open spaces can be the peaks. The open spaces can be substantial in terms of oral fluid flow substantial in terms of oral fluid flow & bacterial invasion.& bacterial invasion.

The luting cement can seal the space The luting cement can seal the space & provide void- free sealed & provide void- free sealed continium; so it resists shear stress continium; so it resists shear stress acting along the interface acting along the interface (mechanical retention)

It can also It can also bind chemically bind chemically to to tooth structure & restoration so it tooth structure & restoration so it improves the retention of prosthesis.improves the retention of prosthesis.

Continue/AnswerContinue/Answer

In mechanical retention , failure In mechanical retention , failure occurs at interfaces . While in occurs at interfaces . While in chemical retention , failure occurs chemical retention , failure occurs cohesively through the cement itself.cohesively through the cement itself.

Ideal Luting CementIdeal Luting Cement

Adheres to tooth structure & cast alloysAdheres to tooth structure & cast alloys Long working timeLong working time Low viscosity & solubilityLow viscosity & solubility Nontoxic to the pulpNontoxic to the pulp Adequate strength propertiesAdequate strength properties Compressible in thin layersCompressible in thin layers Provides good sealProvides good seal Any excess can be easily removedAny excess can be easily removed

Zinc Phosphate cementZinc Phosphate cement

Powder : Powder : Zinc oxide Zinc oxide (90%) & (90%) & magnesium oxide (10%)magnesium oxide (10%)

Liquid : Liquid : Phosphoric acid Phosphoric acid , , water , aluminium phosphate , water , aluminium phosphate , zinc phosphate.zinc phosphate.

Acid content 33 ± 5 wt%Acid content 33 ± 5 wt%


Reduction in P/L ratio produces weaker Reduction in P/L ratio produces weaker cementcement

Loss or gain in water content of liquid Loss or gain in water content of liquid leads to weaker cementleads to weaker cement

film thickness is about film thickness is about 25µm25µm Bonding occurs by Bonding occurs by mechanical mechanical

interlocking at interfaces interlocking at interfaces Working time Working time 1.5 to 5 min .Setting time 1.5 to 5 min .Setting time

2.5 – 8 min2.5 – 8 min


Excess cement can be easily Excess cement can be easily removed after it has setremoved after it has set

Maturation (It is advisable to place a Maturation (It is advisable to place a layer of varnish to margin to allow layer of varnish to margin to allow the cement more time to mature )the cement more time to mature )


Limited biocompatibility :Limited biocompatibility :

2 minutes after mixing pH is 22 minutes after mixing pH is 2

pH is 5.5 at 24 hrpH is 5.5 at 24 hr

irritation depends on the irritation depends on the thickness thickness of residual dentin, because of this of residual dentin, because of this irritation cavity varnish may be used irritation cavity varnish may be used to protect against the pulp irritation to protect against the pulp irritation


Successful use over many years Successful use over many years suggests that its effect on dental pulp suggests that its effect on dental pulp is is clinically acceptableclinically acceptable

The luting agent of choice for The luting agent of choice for otherwise normal conservatively otherwise normal conservatively prepared toothprepared tooth

QuestionQuestion

How can we increase the How can we increase the working time of zinc working time of zinc phosphate cement at phosphate cement at

chairside ?chairside ?

Zinc Polycarboxylate Zinc Polycarboxylate cementcement

Liquid is an aqueous solution Liquid is an aqueous solution polyacrylic polyacrylic acid or a copolymer of acid or a copolymer of acrylic acid with other carboxylic acrylic acid with other carboxylic acids , such as itaconic acidacids , such as itaconic acid

Powder is similar to that of zinc Powder is similar to that of zinc phosphate cement ± stannous phosphate cement ± stannous flourideflouride


11stst cement system that developed an cement system that developed an adhesive bond to tooth structureadhesive bond to tooth structure

Bonding to tooth structure Bonding to tooth structure is explained is explained by :by :

Polyacrylic acid reacts with calcium ions Polyacrylic acid reacts with calcium ions via carboxyl groups on the surface of E via carboxyl groups on the surface of E or D.or D.

Binds chemiclly to Stainless Steel crowns .Binds chemiclly to Stainless Steel crowns .


Zinc polycarboxylate mix is classified Zinc polycarboxylate mix is classified a pseudoplastic a pseudoplastic (thixotropic(thixotropic)& )& undergoes thinning at increased undergoes thinning at increased

shear shear rate…rate…25µm .25µm .


Working time 2.5 min compared Working time 2.5 min compared with approx. 5 min of zinc phosphatewith approx. 5 min of zinc phosphate

( refrigerate powder before mixing)( refrigerate powder before mixing)

Compressive s. 55 to 67Compressive s. 55 to 67

MOE 2.4 to 4.4 GPa MOE 2.4 to 4.4 GPa


Removal of excess cement is more Removal of excess cement is more difficult difficult than zinc phosphate than zinc phosphate cement after it has setcement after it has set

Avoid removing excess cement in Avoid removing excess cement in the rubbery stage the rubbery stage because cement because cement may be pulled out from beneath may be pulled out from beneath the margins leaving a voidthe margins leaving a void

You can remove You can remove it after it has set it after it has set or ASA seating is completedor ASA seating is completed


Relatively biocompatible Relatively biocompatible (equivalent to (equivalent to ZOE) because :ZOE) because :

I.I. pH rises more rapidly pH rises more rapidly

II.II. Larger size of polyacrylic acid molecule Larger size of polyacrylic acid molecule so less diffusion into dentinal tubules.so less diffusion into dentinal tubules.

Recommended on retentive preparation Recommended on retentive preparation when mimimal pulp irritation is when mimimal pulp irritation is important ( in children with large pulp important ( in children with large pulp horns)horns)

Glass Ionomer CementGlass Ionomer Cement Powder is an Powder is an acid-soluble calcium acid-soluble calcium

flouroaluminosilicate flouroaluminosilicate glass(15 to 50µm)glass(15 to 50µm) Liquid is an aqueous solutions of Liquid is an aqueous solutions of polyacrylic polyacrylic

acid acid 40 to 50%wt + tartaric acid40 to 50%wt + tartaric acid

Water-settable glass ionomer Water-settable glass ionomer : : freeze-dried freeze-dried polyacid powder & glass powderpolyacid powder & glass powder are placed are placed in the same bottle as a powder, the liquid in the same bottle as a powder, the liquid consists of water .When mixed, acid consists of water .When mixed, acid dissolves to a liquid acid & this is followed dissolves to a liquid acid & this is followed by acid-base rxn.by acid-base rxn.

Glass Ionomer CementGlass Ionomer Cement

Both Both dessication & dessication & contamination contamination compromise the compromise the integrity of freshly mixed integrity of freshly mixed material(should be protected material(should be protected with a foil of resin coat or with a foil of resin coat or varnish or by leaving a band of varnish or by leaving a band of cement undisturbed for 10 cement undisturbed for 10 minutes)minutes)


The adhesive mechanism The adhesive mechanism to to tooth structure is comparable to tooth structure is comparable to that of zinc polycarboxylate that of zinc polycarboxylate cement.cement.

F ions released from GIC F ions released from GIC inhibit inhibit the progression of secondary the progression of secondary caries(not documented caries(not documented clinically)clinically)


Removal of excess cement is Removal of excess cement is the same as for the same as for polycarboxylate cement.polycarboxylate cement.


The set cement is somewhat The set cement is somewhat translucenttranslucent

Relatively biocompatibleRelatively biocompatible

( Zinc phosphate<GIC<ZOE )( Zinc phosphate<GIC<ZOE )

Compressive s. is comparable to that Compressive s. is comparable to that of zinc phosphate cement , tensile s. of zinc phosphate cement , tensile s. is higheris higher

Resin-modified glass Resin-modified glass ionomer cement (Hybrid ionomer cement (Hybrid

Ionomer)Ionomer) Among the most popular materials in Among the most popular materials in

general practice general practice Less susceptible to early moisture Less susceptible to early moisture

exposureexposure Low solubility & low micoleakageLow solubility & low micoleakage Less post-treatment sensitivityLess post-treatment sensitivity Should be avoided with all-ceramic Should be avoided with all-ceramic

restorations restorations because they have been because they have been associated with fracture (due to water associated with fracture (due to water absorption & expansion)absorption & expansion)

Resin CementsResin Cements

The composition is similar to that of resin The composition is similar to that of resin –based composite filling material: resin –based composite filling material: resin matrix with silane-treated inorganic fillersmatrix with silane-treated inorganic fillers

Most of them require dentine bonding Most of them require dentine bonding agentagent

The adhesive monomer incorporated in The adhesive monomer incorporated in bonding agent & resin cement includes bonding agent & resin cement includes HEMA , 4-METAHEMA , 4-META

Chemical-cure , light-cure , dual-cure Chemical-cure , light-cure , dual-cure systemsystem


Insoluble in oral fluidsInsoluble in oral fluids strongest in compressionstrongest in compression Less biocompatible Less biocompatible than glass than glass

ionomer cement , especially if they ionomer cement , especially if they are not fully polymerized (the are not fully polymerized (the monomeric component)monomeric component)

Greater film thicknessGreater film thickness


Luting agent of choice Luting agent of choice for all for all ceramic inlays, crowns , bridges ceramic inlays, crowns , bridges (because of their ability to reduce (because of their ability to reduce fracture of ceramic structure & fracture of ceramic structure & because of the range of shades because of the range of shades available to produce an optimal available to produce an optimal esthetic result)esthetic result)

Indicated when a casting has Indicated when a casting has become displaced through lack of become displaced through lack of retentionretention


Chemical-cure resin cementsChemical-cure resin cements

The two components are mixed on a The two components are mixed on a paper pad for 20 to 30 s paper pad for 20 to 30 s

It is best to remove excess cement It is best to remove excess cement immediately after the prosthesis is immediately after the prosthesis is seatedseated

It is suitable for It is suitable for all types of prosthesesall types of prostheses


Light –curable cementsLight –curable cements

Single component systemSingle component system

Indicated for cementation of Indicated for cementation of thin ceramic thin ceramic prostheses, prostheses, resin-based prostheses, & resin-based prostheses, & direct bonding of ceramic and plastic direct bonding of ceramic and plastic orthodontic brackets orthodontic brackets when the thickness when the thickness is less than 1.5mmis less than 1.5mm

Excess cement should be removed ASA Excess cement should be removed ASA seating is completedseating is completed


Dual-cure cementsDual-cure cementsTwo- component systemsTwo- component systemsChemical activation is v slow & Chemical activation is v slow &

provides extended working time provides extended working time until the cement is exposed to curing until the cement is exposed to curing lightlight

Should not be used with light –Should not be used with light –transmitting prostheses transmitting prostheses thicker than thicker than 2.5mm 2.5mm

Zinc Oxide –Eugenol Zinc Oxide –Eugenol CementCement

Setting rxn:Setting rxn:

Zinc oxide hydrolysis & subsequent Zinc oxide hydrolysis & subsequent rxn betw. zinc hyroxide & eugenol to rxn betw. zinc hyroxide & eugenol to form a chelateform a chelate

Water is needed to initiate the rxn & it Water is needed to initiate the rxn & it is a by-product of rxn (rxn proceeds is a by-product of rxn (rxn proceeds more rapidly in a humid more rapidly in a humid environment)environment)

Least irritating of all dental Least irritating of all dental cements cements (pH 7) (pH 7) & excellent & excellent seal, seal, free eugenol has free eugenol has bacteriocidal & obtudent bacteriocidal & obtudent effecteffect


Should be used only in restorations Should be used only in restorations with good inherent retention form with good inherent retention form where emphasis is on where emphasis is on biocompatibility & pulpal biocompatibility & pulpal protectionprotection


Residual free eugenol interferes Residual free eugenol interferes with proper setting of resin with proper setting of resin cements ;cements ;carboxylic acid carboxylic acid can be can be used to replace eugenol & used to replace eugenol & produce produce zinc oxide-noneugenol zinc oxide-noneugenol cementscements


iii.iii. Temporary ZOE Temporary ZOE RestorationsRestorationsLast for a few days to few weeks at mostLast for a few days to few weeks at most

iv.iv. Intermediate ZOE Intermediate ZOE RestorationsRestorationsLast for 1 year Last for 1 year Sufficient powder must be added to Sufficient powder must be added to

achieve a stiff, puttylike restorative achieve a stiff, puttylike restorative material.material.

Comparison Comparison between between cementscements

Solubility & Solubility & disintegration of disintegration of

cementscements In vivo studies :In vivo studies :

ZOE > Zinc phosphate / Zinc ZOE > Zinc phosphate / Zinc polycarboxylate > GIC > Resin-polycarboxylate > GIC > Resin-modified GIC > Resin cementmodified GIC > Resin cement

Comparison of film Comparison of film thicknessthickness

Comparison of retentionComparison of retention

Compressive Strength Compressive Strength

Patient sensitivityPatient sensitivity

Radioopacity Radioopacity

Comparison of Comparison of microleakagemicroleakage

Antibacterial prop.Antibacterial prop.

How does the adaptation How does the adaptation of restoration affect of restoration affect

selection of cement ?selection of cement ?

How does the type How does the type of restoration of restoration

affect selection of affect selection of cement?cement?

AnswerAnswer

Adhesion of Zinc polycarboxylateAdhesion of Zinc polycarboxylate to to stainless steel stainless steel is excellentis excellent

Metal restorMetal restoration requires ation requires chemical cure resin chemical cure resin cements , cements , resins formulated for cementing resins formulated for cementing conventional casting must have conventional casting must have lower film thickness than lower film thickness than materials designed for ceramicsmaterials designed for ceramics

Resin modified glass Resin modified glass ionomer luting ionomer luting agents should be avoided with agents should be avoided with all all ceramic restorations ceramic restorations because they because they have been associated with fracture , have been associated with fracture , which is probably due to their water which is probably due to their water absorption and expansionabsorption and expansion

Adhesive resins Adhesive resins are the luting agents of are the luting agents of choice for all choice for all ceramic inlays, crowns , ceramic inlays, crowns , bridgesbridges (because their ability to reduce (because their ability to reduce fracture of ceramic structure & because fracture of ceramic structure & because of the range of shades available to of the range of shades available to produce an optimal esthetic result)produce an optimal esthetic result)

the mechanism of all ceramic crown the mechanism of all ceramic crown strengthening is due to prevention of strengthening is due to prevention of crack propagation from the internal crack propagation from the internal surface by the bonded resinsurface by the bonded resin

Dual cure is used in ceramics, but it is not Dual cure is used in ceramics, but it is not used for veneers because the amine used for veneers because the amine accelerator can cause the color of luting accelerator can cause the color of luting agent to change , for veneers a light -cured agent to change , for veneers a light -cured resin is preferredresin is preferred

Light curable cements Light curable cements are indicated for are indicated for cementation of thin ceramic prosthesis , the cementation of thin ceramic prosthesis , the thickness of the restoration in the bonded thickness of the restoration in the bonded area is area is less than 1.5 mmless than 1.5 mm

For inlays, a chemical or dual cure resin For inlays, a chemical or dual cure resin cement is preferredcement is preferred

Zinc phosphate and polycarboxylate Zinc phosphate and polycarboxylate cements are not recommended to be cements are not recommended to be used with used with all ceramic all ceramic restorations restorations because the materials are opaque because the materials are opaque due to high concentration of due to high concentration of unreacted zinc oxide , this will unreacted zinc oxide , this will detract from the appearance of detract from the appearance of porcelain crowns , particularly if the porcelain crowns , particularly if the cement luting margin is visiblecement luting margin is visible

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Luting Cements Rola Shadid, BDS, MSc, Associate fellow AAID